The subject matter disclosed herein relates to a flow balancing slot.
Tip clearance losses in a turbine bucket typically constitute 20-25% of the total losses in the blade row. These losses generally occur due to high energy flow escaping through the clearance region without doing any useful work, mixing of tip leakage flow and passage flow downstream of the bucket and flow from the pressure surface of the airfoil crossing over to the suction surface. A lift force generated by the airfoil and a torque on the blade row are, thus, reduced.
The instance of flow crossover has been addressed by the installation of a cover on the bucket. The cover diverts flow away from the crossover region and decreases the losses associated with crossover flow.
The shape and size of the cover can influence the amount of the flow that is diverted and can thereby influence the level of the decreased losses. Unfortunately, mechanical constraints often require the cover to be scalloped and the scallop introduces an additional loss in the form of intrusion losses. Intrusion losses result from the in-out flow through the scallop and further increase downstream mixing losses. That is, in conventional bucket covers, flow leaving from an aft scallop region of the bucket cover re-enters the main flow and interacts with a horseshoe vortex propagating therein and, thus, increases a size and intensity of a flow-mixing loss region.